This invention relates to computing weighing scales, particularly scales of the type used in grocery stores, delicatessens, etc., to weigh random weight items, and to calculate the total price or total value of such items, based upon predetermined price per unit weight for the particular type of article or commodity. A typical form of prior art scale is disclosed in U.S. Pat. No. 3,741,324 of June 26, 1973, which has separate electronic digital indicators for price per unit weight and total price, and an optical weight display. A later version of that scale, known commercially as the Hobart Model 1500 Electronic Checkstand Scale, utilizes the same platter, weighing mechanism including weight readout and code generating mechanism, and includes provisions for transmitting weight data (on command) to a remote computer and optionally to a remote digital electronic weight display. That display, visible to the operator and the customer, shows only the weight of the item. A multistation version of this scale, utilizing a common computer system and individual displays for weight, price per unit weight and total price is disclosed in U.S. Pat. No. 3,906,208 issued Sept. 16, 1975.
For many years the so called "computing scales" of the drum computer type have been used in various types of food markets, etc. These incorporate a mechanical computing mechanism in the form of a moving chart, usually a rotating cylinder as typically shown in U.S. Pat. Nos. 2,742,811 and 2,880,643, and have a number of different columns related to corresponding price per unit weight. In these scales an indicator tape or wire is visually aligned along the chart by the operator, when the scale comes to rest, to read from the chart the weight of an article on the scale, and from the appropriate column total price or value. The operator then manually writes some or all of this information, in many cases just the total price, on the package used to wrap or cover the weighed item. In these scales the full chart is often visible only to the operator, and the customer sees only a weight display, and that from a vantage point where accurate alignment may be difficult. The computation capability in these prior art scales is of course limited by the number of chart columns. Such scales are not readily connected even to small in-store computers, and they are essentially an independent weighing device.
In order to simplify and conserve the cost of readout devices for electronic computing scales, it is desirable to utilize a minimum number of more or less conventional components, without sacrificing the capability for accurate weight readout, simplification of data entry, safeguarding against operator error (unintentional or otherwise), and display clearing of data for both the customer and the operator.
The broad concept of multi-purpose seven-segment numerical displays (or equivalent) which are utilized in the scale of the present invention, together with identification of the data being displayed, is disclosed in U.S. Pat. No. 3,580,421 which relates to liquid dispensing, e.g., a gasoline pump. In this gasoline pump application of multi purpose numerical displays there is infrequent change of the price per unit factor (cents/gal.), and thus no need for quick entry or quick change of this information. There is also in the gasoline pump no requirement to recognize the end of the quantity measurement (gallons) since there is no problem of sensing when the quantity is fully dispensed; the tank is either full, or a predetermined quantity has been pumped. In a similar manner, in the gasoline pump entry of the unit price factor precedes dispensing of a random quantity and computation proceeds as liquid is dispensed. Moreover, in the gasoline pump none of the dispensed material will be removed, so the quantity measurement is always unidirectional, and not subject to either plus or minus variations as when a customer wants some of a commodity taken from a scale platter weight is displayed.
In computing weighing scales, especially scales used in random weight measurement and total price calculation of many different items, the price per unit weight will frequently change, and the quantity (weight) may be changed up or down when the operator, or customer, observes the actual displayed weight and before total price computation occurs, and it may also be necessary to adjust for tare weight of a package. In computing scales, moreover, the "weights and measures" regulations of various governmental bodies require compliance, and the competitive nature of the scale business makes cost a significant factor. Thus, the adaptation of a single multipurpose multi-digit indicator to a computing scale presents unique and unobvious requirements.